Captures flagged X-Blank-Suspected are not billed, which is the right
default: a white frame is not what anyone paid for.
With no cap, it was also an input an attacker controls. A caller who controls the target page can serve an empty document and render free forever, and the flag itself could be forced on real content through a narrow selector, a huge viewport or a quality-1 JPEG.
Unbilled blanks are now capped at 10% of the plan's monthly volume, minimum 50.
Past the cap a flagged capture bills like any other, because the image was
still delivered. Every response says which it was in X-Billed.